KR20230093666A - Methods of preparing spherical silicas and spherical silicas preparing therefrom - Google Patents

Abstract

The present invention comprises the steps of stirring water glass, nonionic surfactant, and oil to form a stable emulsion; Dropping the stirred emulsion into a mixed solution of nitric acid and a gelling agent (NH4HCO3); heating at 75 to 85° C. for 0.5 to 1 hour; A method for producing spherical silica comprising the steps of removing trace amounts of oil through ultrasonic waves and microwaves, rapidly solid-liquid separation through a physical continuous separation process, and filtering, washing, and drying, and spherical silica prepared therefrom. According to the method of the present invention, spherical silica with improved oil absorption ability can be prepared using a W/O emulsion system using water glass, a nonionic surfactant, and oil. In addition, process efficiency can be increased by reducing process time by 75% compared to existing processes.

Description

Method for preparing spherical silica and spherical silica prepared therefrom {Methods of preparing spherical silicas and spherical silicas preparing therefrom}

The present invention relates to a method for producing spherical silica, using water glass as a raw material, using a w/o emulsion system, and adding the water glass emulsion dropwise to a mixture of nitric acid and a gelling agent and reacting in one step to prepare silica with improved oil absorption capacity, and It relates to a technology for shortening the process time by reducing the oil removal process time using a physical method.

Spherical silica is a super-porous material in which nano-sized silica (SiO2) particles form a three-dimensional network structure and has a porosity of over 95%. The pore volume is very large and the thermal conductivity, dielectric constant, and refractive index are very low. It can be usefully applied to various fields such as various carriers, low dielectric coating films, and antireflection films.

In general, spherical silica is prepared by preparing a wet gel from a silica precursor such as water glass, and removing liquid components inside the wet gel without destroying the microstructure. The form of the target silica airgel can be divided into three types: powder, granule, and monolith, and is generally manufactured in the form of powder.

Korean Patent No. 10-1310286 suggested a method for preparing spherical silica powder by preparing a high-purity silica sol from a water glass solution using an ion exchange resin, followed by solvent substitution and surface modification. However, the above invention has disadvantages such as high price due to low productivity because long-time solvent replacement and surface modification processes are necessarily required, and not suitable for mass production due to the fact that ion exchange resin is used.

In addition, in the existing process as shown in FIG. 1, a long time of 24 hours is required in the oil removal process, which lowers process efficiency.

Accordingly, efforts have been made to improve productivity by shortening the process time, to control the porosity of the spherical silica to be produced, and to improve the oil absorption capacity, and have reached the present invention.

In the present invention, in the method for preparing spherical silica by dropping droplets of water glass from a W / O emulsion system using water glass, a nonionic surfactant and oil, a method for preparing spherical silica with improved oil absorption capacity and shortening the process time want to provide

In addition, the present invention is to provide a spherical silica with improved oil absorption capacity prepared by the above production method.

The present invention comprises the steps of stirring water glass, nonionic surfactant, and oil to form a stable emulsion; Dropping the stirred emulsion into a mixed solution of nitric acid and a gelling agent (NH4HCO3); heating at 75 to 85° C. for 0.5 to 1 hour; Provided is a method for producing spherical silica, which includes removing trace amounts of oil through ultrasonic waves and microwaves, rapidly solid-liquid separation through a physical continuous separation process, and filtering, washing, and drying.

In addition, the present invention provides a spherical silica prepared by the above method.

According to the present invention, silica with improved specific surface area and oil absorption ability can be produced by using water glass as a raw material, using a w/o emulsion system, and adding the water glass emulsion dropwise to a mixture of nitric acid and a gelling agent to react in one step. In addition, by reducing the oil removal process time using a physical method, the process efficiency can be increased by reducing the process time by more than 75% compared to the existing process.

1 is a flow chart of an existing process.
2 is a process flow diagram of the manufacturing method of the present invention.
3 is a schematic process diagram of the manufacturing method of the present invention.
Figure 4a is a SEM picture of the spherical silica prepared in Example 1.
Figure 4b is a SEM picture of the spherical silica prepared in Comparative Example 1.

The present invention is a process using a W / O emulsion system in synthesizing spherical silica / silicate, specifically, forming a stable emulsion by stirring water glass, a nonionic surfactant, and oil; Dropping the stirred emulsion into a solution of nitric acid and a gelling agent (NH4HCO3); heating at 75 to 85° C. for 0.5 to 1 hour; Provided is a method for producing spherical silica, which includes rapidly solid-liquid separation by a physical continuous separation process of ultrasonic waves and microwaves, and filtration, washing, and drying, and spherical silica prepared therefrom.

The water glass is composed of a small amount of Fe2O3 in addition to Na2O·nSiO2 (n = 2 to 4), and the water content is 10 to 30%. Water glass is a strong alkali, and silica gel is made by drying the precipitate produced by neutralizing it with an acid. In the present invention, the pores of the spherical silica produced can be adjusted by adjusting the concentration of water glass, which is a raw material, and thus the oil absorption capacity of the silica can be improved.

The preferred concentration of the water glass proposed in the present invention is to be included in the range of 14.5 to 22.13% (SiO2% w/w %) based on the SiO2 content in the water glass. The oil absorption capacity of the spherical silica prepared when using water glass in an amount adjusted to the concentration in the above range was confirmed to be in the range of 140 to 191 g/100 g. In addition, the water glass is preferably aged at a temperature of 30 to 50 ° C. for 24 hours before use, and in this case, the surface of the prepared silica is smooth and has less by-products.

In the present invention, the amount of oil absorption is determined by the size and specific surface area of the silica particles. The size of the silica particles is determined by the temperature, the rpm of the homomixer, and the type of surfactant or concentration of nonionic surfactant/oil in the emulsion. The range for each condition is described as follows. The temperature is 10 ~ 25 ℃, the rpm of the homomixer is 3,500 ~ 5,000 rpm, and the nonionic surfactant / oil concentration is 5 ~ 15%.

Representative examples of the oil include kerosin or paraffin oil, and diesel p-xylene, hexane, or a mixture thereof may be used. The weight ratio of the mixed solution of oil and nonionic surfactant and water glass may be 0.34 to 1.

A surfactant is a substance that is adsorbed on the surface of a liquid to increase the activity of the interface and significantly change its properties. . In the present invention, a nonionic surfactant is used as a surfactant, specifically (sorbitan monooleate, sorbitan monostearate, sorbitan monopalmitate and sorbitan It may be one or more selected from the group consisting of monolaurate (sorbitan monolaurate) These surfactants are preferably included in the weight range of 0.16 to 3% in the emulsion.

When the oil and the nonionic surfactant are first mixed, and water glass is added thereto and stirred using a homomixer, a stable emulsion is formed. Stirring is preferably carried out at a speed of 3,000 to 6,000 rpm for 10 to 30 minutes to stabilize the emulsion, and the temperature range is 10 to 40 °C. At this time, the physical energy (stirring force) applied to the emulsion is stored as surface energy and is characterized by being maintained as an emulsion even after several hours. In addition, the size of the emulsion sphere is determined by the rpm speed, the temperature of each fluid (oil and water glass), the concentration of the water glass, and the concentration of the surfactant, and the size ranges from 3 to 100 μm.

The nitric acid (HNO3) solution and the gelling agent (NH4HCO3) solution are solutions containing 9 to 13% by weight of the gelling agent in 10 to 15% by weight of nitric acid, respectively. The order of making this solution is prepared by dropping the nitric acid solution into the gelling agent, and the bubbles generated at this time are carbon dioxide (CO2). To this, the emulsion stabilized by the stirring is slowly added dropwise.

Then, the solution of nitric acid and gelling agent (NH4HCO3) containing the loaded emulsion is heated for 0.5 to 1 hour after reaching 75 to 85°C. As the temperature rises, the stored surface energy undergoes phase separation again, and the temperature at this time is called the temperature at which hydrophilic and lipophilic properties equilibrate (PIT, Phase Inversion Temperature). In the above reaction, the PIT range is reached in the range of 30 to 50 ° C, and almost completely separated at 75 ° C. In the emulsion solution (SiO2 + oil + surfactant) dropped in the PIT range, the lipophilic phase (oil + surfactant) is separated and moves to the upper layer due to the density difference. At that moment, the remaining water glass droplets immediately react with the hydrophilic phase (nitric acid, gelling agent) and gelate into a spherical shape.

When the reaction is complete, there are a total of three phases, the uppermost layer is an oil and nonionic surfactant layer, followed by water, and then a layer containing water and solids. At this time, using the difference in density between the water and oil layers, only the water and solids in the lower layer are taken out. Water and solids contain trace amounts of oil components.

In order to completely remove trace amounts of oil components, a solution containing water and solid components is re-separated from solid components using ultrasonic waves and microwaves. Ultrasound is preferably performed at a temperature of 70 ° C. or higher for 60 to 70 seconds, and then microwaves in a wavelength range of 26 to 28 kHz are irradiated for 1 to 3 hours. At this time, the temperature of the aqueous solution containing the solid content rises from 70 ° C to 90 ° C, and a small amount of oil component moves to the upper layer. Then, using a separatory funnel, drain the water and solids again.

Solid-liquid separation is performed by filter filtration or centrifugation. In this process, silica containing about 67 to 80% of water is obtained. At this time, water washing is repeated until the conductivity and pH are 100 mS/m or less, respectively, and the pH is 7 to 8.

Through this process, spherical silica in a solid state is obtained, and finally, they are dried (moisture content of 5% or less) to complete the preparation of the spherical silica of the present invention. The washing is performed with water (tap water, industrial water). The drying may be performed in a box oven, hot air drying or microwave drying process.

The manufacturing method of the present invention can effectively remove oil and shorten the process time by using ultrasonic waves and microwaves in the oil removal process. That is, since the oil removal process, which took 24 hours in the existing process (FIG. 1), can be completed in 1 to 3 hours, the total process time is reduced (FIG. 2).

The spherical silica of the present invention thus prepared shows an improved oil absorption. Therefore, the spherical silica of the present invention can be advantageously used as cosmetic, semiconductor and resin fillers.

Hereinafter, the present invention will be described in more detail through examples.

Example 1

Spherical silica was prepared according to the process shown in FIG. 3 .

Water glass No. 3 (sodium silicate, Ilshin Chemical, silica content 28-30% by weight, SiO2:Na2O = 3.52:1) and distilled water were diluted to prepare a water glass solution with a SiO2 content of 14.5% by weight, and after aging for 24 hours, filter prepared by Kerosine and the surfactant sorbitan monooleate (SPAN 80, HLB=4.3) were mixed to form a mixed solution, and then prepared water glass was added thereto.

Next, the emulsion was stirred for 30 minutes at a stirring speed of 4,500 rpm and 10 °C to stabilize the emulsion. Thereafter, while stirring the mixture of nitric acid and NH4HCO3 solution at 100 rpm, the emulsion stabilized by the stirring was added dropwise at a constant speed.

Then, a solution of nitric acid and gelling agent (NH4HCO3) containing the loaded emulsion was heated at 80 DEG C for 1 hour. The reactants were sufficiently settled, and a solution containing silica was extracted through a lower valve.

The heated solution was sonicated for 60 seconds, and then microwaves in the wavelength range of 26 to 28 kHz were irradiated for 3 hours to re-separate trace amounts of oil.

The separated silica was filtered and washed with water. Finally, spherical silica ('silica product' in FIG. 2) was prepared by drying with hot air at 75 ° C or higher.

Comparative Example 1

Spherical silica was prepared in the same manner as in Example 1, but unaged water glass was used.

4a and 4b are SEM images of spherical silica prepared in Example 1 and Comparative Example 1, respectively. Looking at this, it can be seen that when the silica is produced by aging the water glass, it is produced in a clean and clear spherical shape without any deposits on the silica surface.

Comparative Example 2

Sunjin Beauty Science Co., Ltd.'s SUNSIL-130 product was used as spherical silica.

Example 2

Spherical silica was prepared in the same manner as in Example 1, except that the emulsification stirring speed was 3,000 rpm instead of 4,500 rpm.

Example 3

Spherical silica was prepared in the same manner as in Example 1 except that the emulsification stirring speed was 6,000 rpm instead of 4,500 rpm.

Example 4

Spherical silica was prepared in the same manner as in Example 1 except that the SiO2 content in the water glass was 18.5 wt% instead of 14.5 wt% and the emulsification stirring speed was 3,000 rpm instead of 4,500 rpm.

Example 5

Spherical silica was prepared in the same manner as in Example 1 except that the SiO2 content in the water glass was 18.5 wt% instead of 14.5 wt%.

Example 6

Spherical silica was prepared in the same manner as in Example 1 except that the SiO2 content in the water glass was 18.5 wt% instead of 14.5 wt% and the emulsification stirring speed was 6,000 rpm instead of 4,500 rpm.

Oil absorption, average particle size, D50 and D90 of Examples 1 to 3 and Comparative Examples 2 and 3 were measured. The amount of oil absorption and average particle size were each measured by the test method specified in "General Test Methods for Pigments and Extender Pigments Part 5: Measurement of Oil Absorption". The test method is specifically described in "http://www.kssn.net/StdKS/ks_detail.asp?k1=M&k2=ISO%20787-5&k3=2". The results are shown in Table 1.

item Details Example 1 Comparative Example 2 Example 2 Example 3 Example 4 Example 5 Example 6 Main synthesis conditions SiO2 content in water glass 14.5% Third party product 14.5% 14.5% 18.5% 18.5% 18.5% Water glass aging O - O O O O O Emulsion stirring speed (rpm) 4,500 Third party product 3,000 6,000 3,000 4,500 6,000 Analysis oil absorption
(g/100g) 163.3 111.13 153.17 170.9 130.76 140.7 145.7 average particle size
(μm) 7.78 7.2 18.84 4.91 16.95 4.98 4.46 D50
(μm) 6.36 6.8 6.18 4.74 14.89 4.66 3.58 D90
(μm) 14.1 10.6 34.76 6.18 31.22 7.35 8.51

As shown in the table above, the spherical silica according to the embodiment of the present invention has an improved oil absorption compared to Comparative Example 2 (competitor's product).

Claims (8)

Stirring water glass, nonionic surfactant, and oil to form a stable emulsion;
Dropping the stirred emulsion into a mixed solution of nitric acid and a gelling agent (NH4HCO3);
heating at 75 to 85° C. for 0.5 to 1 hour;
removing trace amounts of oil through ultrasound and microwave;
Step of rapidly solid-liquid separation with a physical continuous separation process; and
A method for producing spherical silica comprising the steps of filtering, washing, and drying. In paragraph 1,
The method for producing spherical silica, characterized in that the water glass has a concentration in the range of 14.5% to 22.13% (SiO2% w/w%) based on the SiO2 content in the water glass. In paragraph 1,
The nonionic surfactant is from the group consisting of sorbitan monooleate, sorbitan monostearate, sorbitan monopalmitate and sorbitan monolaurate. Characterized in that at least one selected, a method for producing spherical silica. In paragraph 1,
The method for producing spherical silica, characterized in that the oil is kerosin or p-xylene, or a mixture thereof. In paragraph 1,
The method for producing spherical silica, characterized in that the water glass is aged at a temperature of 30 to 50 ° C. for 24 hours and filtered before use. In paragraph 1,
The stirring is a method for producing spherical silica, characterized in that for 0.5 to 1 hour at a rate of 3,000 to 6,000 rpm at a temperature of 10 ~ 40 ℃. In paragraph 1,
The method for producing spherical silica, characterized in that the separation process by ultrasonic waves and microwaves is performed for 1 to 3 hours. Spherical silica, characterized in that produced by the method of any one of claims 1 to 7.

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